1. Field of the Invention
The present invention relates to monopole antennas for radiating electromagnetic signals and, more particularly, to a printed monopole antenna including at least one radiating element formed on one side of a printed circuit board having an electrical length where the radiating element has a primary resonance within a first frequency band and a parasitic element formed on the opposite side of the printed circuit board designed to tune a secondary or higher mode resonant response of the radiating element within a second frequency band.
2. Description of Related Art
It has been found that a monopole antenna mounted perpendicularly to a conducting surface provides an antenna having good radiation characteristics, desirable drive point impedance, and relatively simple construction. As a consequence, monopole antennas have been utilized with portable radios, cellular telephones, and other personal communication systems. To date, however, such monopole antennas have generally been limited to wire designs (e.g., the helical configuration in U.S. Pat. No. 5,231,412 to Eberhardt et al.), which operate at a single frequency and associated bandwidth.
In order to minimize size requirements and permit multi-band operation, microstrip and lamina antennas have been developed for use with certain communication applications. More specifically, U.S. Pat. No. 4,356,492 to Kaloi discloses a microstrip antenna system including separate microstrip radiating elements which operate at different and widely separated frequencies while being fed from a single common input point. However, these radiating elements are directly connected with each other and require a ground plane which fully covers the opposite side of a dielectric substrate from such radiating elements. Clearly, this design is impractical for monopole antenna applications, and indeed functions in a completely different manner. Likewise, the lamina antennas disclosed by U.S. Pat. Nos. 5,075,691 and 4,800,392 to Garay et al. require both a direct connection between radiating elements and a ground plane in order to provide multi-band operation.
Further, U.S. Pat. No. 5,363,114 to Shoemaker discloses a planar serpentine antenna which includes a generally flat, non-conductive carrier layer and a generally flat radiator of a preselected length arranged in a generally serpentine pattern secured to the surface of the carrier layer. One form of this antenna has a sinuous pattern with radiator sections in parallel spaced relation in order to provide dual frequency band operation. However, it is seen that the two frequencies at which resonance takes place involves the length of each radiator section and the total length between first and second ends. While this arrangement is suitable for its intended purpose, it likewise is incapable of operating in the fashion of a monopole or dipole antenna.
Accordingly, it would be desirable for a monopole antenna to be developed which not only is operable within more than one frequency band, but also avoids the associated limitations of microstrip and lamina antennas. Further, it would be desirable for a printed monopole antenna to be developed which operates at more than one frequency band and is configured to require only a single radiating element.
In light of the foregoing, a primary object of the present invention is to provide a monopole antenna which is operable within more than one frequency band.
Another object of the present invention is to provide a monopole antenna which can be constructed within very tight tolerances.
Still another object of the present invention is to provide a printed monopole antenna operable within more than one frequency band.
Yet another object of the present invention is to provide a monopole antenna which eliminates ground plane requirements found in microstrip and lamina antennas.
Another object of the present invention is to eliminate direct electric connection between radiating elements of multi-band antennas.
Still another object of the present invention is to provide a printed monopole antenna operable within more than one frequency band that requires only a single radiating element.
A further object of the present invention is to provide a printed monopole antenna which tunes the secondary resonance of a radiating element within a second specified frequency band.
Yet another object of the present invention is to provide a printed monopole antenna which can be easily configured for various frequency bands of operation.
These objects and other features of the present invention will become more readily apparent upon reference to the following description when taken in conjunction with the following drawing.